Liquid crystal display devices are widely used in a variety of personal computers and the like. Lately, the demand for the liquid crystal display devices has been increasing.
In the recent liquid crystal display devices, there has been a demand in that the back-light is to be thin, a high precision image is to be displayed, and a high brightness image is to be displayed. Using a thin back-light and displaying a high precision image are likely to result in a low brightness image.
To establish a thin back-light, a high precision image, and a high brightness image, it is desirable that the utility efficiency of light is improved so as to compensate brightness. As a specific unit for improving brightness, a brightness enhancing film (reflective polarizer) has been suggested. The brightness enhancing film is largely classified into a linearly polarized light-separating type (for example, see JP-A-4-268505, JP-T-9-507308 and JP-T-10-511322) and a circularly polarized light-separating type (for example, see JP-A-8-271837, JP-A-8-271731, JP-A-10-321025, JP-A-11-174230 and JP-A-11-248942). Any of the brightness enhancing films are installed between a lower polarizer (light absorbing polarizer) and a light source (back-light).
By utilizing the brightness enhancing film, the utility efficiency of light in a liquid crystal display device is remarkably improved, which make it possible to considerably decrease electric power consumption.